1. Field of the Invention
The present invention relates to a semiconductor device which is suitable for use in a power converter, such as an inverter.
2. Description of the Background Art
FIG. 10 is a vertical section showing a semiconductor device according to a conventional example as a background of the present invention. This semiconductor device 151 is formed as a vertical n-channel IGBT. The semiconductor substrate 200, a silicon substrate, comprises an n region 201, a p collector region 202, p base regions 203, and n source regions 205. These semiconductor regions 201 to 203 and 205 are formed by selectively introducing p-type and n-type impurities into the pair of main surfaces of the n-type substrate forming the n region 201. In the n-type substrate, the region where the semiconductor regions 201 to 203 and 205 are absent corresponds to the n region 201.
The p collector region 202 is formed selectively and exposed in the lower main surface of the semiconductor substrate 200. The p base regions 203 are selectively formed and selectively exposed in the upper main surface of the semiconductor substrate 200. The n source regions 205, shallower than the p base regions 203, are selectively formed inside the p base regions 203 and selectively exposed in the upper main surface of the semiconductor substrate 200.
The semiconductor device 151 further comprises gate electrodes 206, gate insulating films 207, insulating films 208, emitter electrodes 209, and a collector electrode 211. Each gate electrode 206 faces a channel region with the gate insulating film 207 interposed therebetween; the channel region is a part of the exposed surface of the p base region 203 that is interposed between the n region 201 and the n source regions 205. Each emitter electrode 209 is connected to the exposed surface of the p base region 203 and the n source regions 205 in the upper main surface of the semiconductor substrate 200. The insulating films 208 electrically insulate the gate electrodes 206 and the emitter electrodes 209. The collector electrode 211 is connected to the lower main surface of the semiconductor substrate 200 where the p collector region 202 is exposed.
In the use of the semiconductor device 151 as IGBT, with a positive collector voltage, relative to the emitter electrodes 209, applied to the collector electrode 211 (usually through a load), a gate voltage, relative to the emitter electrodes 209, is applied to the gate electrodes 206. When a positive gate voltage exceeding the threshold voltage is applied, an inversion layer is formed in the channel region, and electrons (the black dots in FIG. 10) are injected into the n region 201 and holes (the white dots in FIG. 10) are then injected from the p collector region 202 into the n region 201. As a result, a phenomenon known as conductivity modulation takes place in the n region 201, which causes the collector electrode 211 and the emitter electrodes 209 to become conductive to each other at a low on-state voltage. When the gate voltage is reduced below the threshold voltage (usually zero or negative value), the inversion layer formed in the channel region disappears and the collector electrode 211 and the emitter electrodes 209 are thus cut off.
As described above, the semiconductor device 151 as IGBT is a switching element advantageous because of its low on-state voltage and voltage controllability; however, unlike MOSFET, it does not contain a diode. Accordingly, when used in a power converter like an inverter, the semiconductor device 151 requires a free-wheeling diode provided outside. This produces the problem that the inductance of the interconnection hinders high-speed switching, and also makes the manufacturing process complicated and causes the applied equipment, such as a power converter, to be large-sized.
To solve these problems, Japanese Patent Application Laid-Open No.5-152574(1993) (which is hereinafter referred to as a first reference) discloses a semiconductor device in which semiconductor regions belonging to the IGBT and semiconductor regions belonging to the free-wheeling diode are disposed in different portions in a single semiconductor substrate. FIG. 11 shows a vertical sectional structure of a semiconductor device 152 and FIG. 12 shows a vertical sectional structure of a semiconductor device 153, both of which are disclosed in the first reference.
Each of the semiconductor devices 152 and 153 has a vertical n-channel IGBT and a vertical diode which are connected in anti-parallel to each other, where a plurality of semiconductor regions belonging to the IGBT and the diode are fabricated in a single semiconductor substrate 200. The semiconductor substrate 200, a silicon substrate, has an IGBT region 220 and a diode region 221 selectively defined in different regions along the pair of main surfaces. An anti-interference region 223 is provided between the IGBT region 220 and the diode region 221 as a region for suppressing interference between them.
The semiconductor substrate 200 has, in the IGBT region 220, part of the n region 201 that belongs to the IGBT, the p collector region 202, p base regions 203, and n source regions 205. The semiconductor substrate 200 also has, in the diode region 221, part of the n region 201 that belongs to the diode, an n+ region 241, and an anode region 204. The n region 201 functions as an n base region in the IGBT region 220 and as a cathode region in the diode region 221. The semiconductor device 152 further has p+ regions 240 and n+ regions 241 selectively formed in the IGBT region 220 and the anti-interference region 223. The semiconductor device 153 has p regions 230 selectively formed in the anti-interference region 223.
On the upper main surface of the semiconductor substrate 200, an anode electrode 210 is connected to the exposed surface of the anode region 204. A cathode electrode 212 is connected to the part of the lower main surface of the semiconductor substrate 200 which belongs to the diode region 221. The emitter electrodes 209 and the anode electrode 210 are connected to each other and the collector electrode 211 and the cathode electrode 212 are integrally coupled.
As described above, the semiconductor devices 152 and 153 each comprise an IGBT and a diode, where the diode connected in anti-parallel to the IGBT functions as a free-wheeling diode associated with the IGBT. Therefore, when the semiconductor device 152 or 153 is applied to a power converter such as an inverter, it is possible, in the assembly of the power converter, to remove the process of separately preparing the IGBT and the free-wheeling diode as separate semiconductor chips and connecting them with interconnection. This also makes the power converter compact. Moreover, since it is not necessary to connect the IGBT and the free-wheeling diode with interconnection, the problem that the switching speed is reduced by the interconnection inductance can be avoided to realize high speed switching.
However, the semiconductor devices 152 and 153 are disadvantageous in that they need the anti-interference region 223 to prevent interference between the IGBT and the diode. The interference between the IGBT and the diode means the phenomenon in which the reverse recovery current generated when the diode performs reverse recovery operation flows from the diode region 221 into the IGBT region 220 to cause a parasitic thyristor in the IGBT to conduct. Preventing the interference requires securing sufficiently large width L for the anti-interference region 223. Therefore the semiconductor devices 152 and 153 require larger area for the semiconductor substrate 200, or larger chip size.
The present invention has been made to solve the aforementioned problems of the conventional technique, and an object of the present invention is to provide a semiconductor device in which a plurality of semiconductor regions belonging to an IGBT and a diode are fabricated in a single semiconductor substrate and which enables reduction of the chip size.
A first aspect of the present invention is directed to a semiconductor device comprising a vertical IGBT and a vertical diode which are connected in anti-parallel with each other, wherein a plurality of semiconductor regions belonging to the IGBT and the diode are fabricated in a single semiconductor substrate. The semiconductor substrate comprises a pair of main surfaces, wherein among the plurality of semiconductor regions, ones that belong to the IGBT are formed in an IGBT region selectively defined along the pair of main surfaces, and ones that belong to the diode among the plurality of semiconductor regions are formed in a diode region selectively defined in a region different from the IGBT region along the pair of main surfaces, and wherein the semiconductor substrate further comprises an electrically insulating partition member selectively formed between the IGBT region and the diode region, for restricting a current flowing from one of the IGBT region and the diode region into the other.
Preferably, according to a second aspect, in the semiconductor device, a trench opening in one main surface of the pair of main surfaces is formed in a portion between the IGBT region and the diode region in the semiconductor substrate, and the partition member comprises an insulator buried in the trench.
Preferably, according to a third aspect, in the semiconductor device, the one main surface of the pair of main surfaces is the main surface on the opposite side to the other main surface where a collector region of the IGBT which belongs to the plurality of semiconductor regions is exposed.
Preferably, according to a fourth aspect, in the semiconductor device, the collector region extends from the IGBT region into the diode region across the portion.
Preferably, according to a fifth aspect, in the semiconductor device, the trench has a bottom reaching the collector region.
Preferably, according to a sixth aspect, in the semiconductor device, another trench is formed in the portion in the semiconductor substrate, the another trench opening in said other main surface and having a bottom protruding from the collector region, and the partition member further comprises another insulator buried in the another trench.
According to the first aspect of the present invention, the electrically insulative partition member effectively reduces interference between the IGBT and the diode, and the width of the ineffective region between the two can be set narrower to reduce the size of the device.
According to the second aspect, the partition member can be formed by a simple process of burying an insulator in a trench formed in the semiconductor substrate. Furthermore, the partition member can be formed in a narrow width and the size reduction of the device can be more effectively achieved.
According to the third aspect, the trench opens in the main surface opposite to the exposed surface of the collector region, so that the trench can be formed during the manufacturing process of forming the semiconductor regions, such as the IGBT""s source region. That is to say, the device offers high productivity.
According to the fourth aspect, the collector region extends from the IGBT region into the diode region across the portion where the trench is formed. Therefore the partition member and the collector region can effectively restrict current flowing from one of the IGBT region and the diode region into the other. That is to say, the interference between the IGBT and the diode can be more effectively suppressed.
According to the fifth aspect, the bottom of the trench reaches the collector region, which still more effectively suppresses the current flowing from one of the IGBT region and the diode region into the other. That is to say, the interference between the IGBT and the diode can be still more effectively suppressed.
According to the sixth aspect, the device further comprises another trench which opens in said other main surface of the semiconductor substrate and has its bottom protruded from the collector region. Thus the insulators buried in the two trenches more effectively restrict the current flowing from one of the IGBT region and the diode region into the other. That is to say, the interference between the IGBT and the diode can be more effectively suppressed.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.